Two-dimensional precise positioning systems are popularly used in precise mechanical processing machines. Related products, such as CCD automatic positioning systems and magnetic induction positioning system are commercially available. Positioning precision of both kinds of devices is around 20 μm.
Telecentric lenses are often used in CCD automatic positioning systems in order to get invariant images in a large scope for precise images comparison and positioning. Although the imaging framework can get better invariant images for positioning, compared images demand sufficient judging features for positioning if a more precise positioning precision is required. In order to achieve sufficient judging features, sampling range needs to be relatively large. Therefore, precision of current mature positioning is around ±20 μm. It is unworkable for the requirement of precise processing machinery. A higher positioning precision is needed for more applications.
Magnetic induction positioning technology utilizes Hall Effect to scan a periodical magnetic positioning template by a magnetic sensing element to get signals of intensity change of a periodic magnetic field by induction. Then, moving distances can be calculated by analyzing the signal. Speed of relative movement of Hall Effect element to the template affects signal intensity change of the magnetic field induction. Hence, when a fast movement needs positioning, magnetic induction positioning precision can not be improved. A mature effective positioning precision is also around 20 μm.
In addition, there are many prior arts about two-dimensional precise positioning system and methods. U.S. Pat. No. 7,042,575 discloses an optical displacement sensor. Please refer to FIG. 1. The invention utilizes light beams to scan a surface and receives optical speckles of the reflected light beams from the surface for further measuring the displacement and locations. It applies mainly to optical mice. For computer input devices, it has an epoch-making meaning. However, coordinates of the scanned object can not be precisely positioned. For application of precise positioning instruments, it doesn't work effectively.
Please refer to FIG. 2. U.S. Pat. No. 7,110,120 provides an optical displacement sensor which can measure a moving body. By scanning an object with light beams directly, separating the scattered light beams reflected from the body by a grating and making the two light beams become two signals with 90° phase difference by a spatial filters, only direction of the displacement can be judged by calculating. In practice, it has no two-dimensional positioning function at all.
U.S. Pat. No. 7,317,538 discloses an optical displacement sensor. Speed of displacement and direction can be obtained by scanning an object with three separated light beams to form three spots on the surface of the object, then calculating scattered light beams from the three spots by analog to digital transform and Fourier transform by Doppler Effect. Please refer to FIG. 3. The method uses complex calculation to measure the speed of displacement and direction of the object. Therefore, reflected light beams have huge affection on the follow-up calculation. Compared with general positioning methods directly using surface features, the '538 patent will have calculation errors caused by data reading and mathematical hypothesis.
Last, please refer to FIG. 4. U.S. Pat. No. 7,242,466 provides a pointing system, for example, an optical mouse, by scanning a pre-coded surface with light beams and receiving scattered light beams from the surface so that movement and location can be further determined. The most notable feature of the invention is the pre-coded surface. With some scattering features and non-scattering features to define a location according to a specified method to arrange a digital pattern, displacement and location of a pointing device receiving scattered light beams relative to a coded surface can be obtained. However, not only is it inconvenient to prepare the pre-coded surface, but also precision is limited.
In summary, current two-dimensional precise positioning systems and methods have several technical inherent problems. The two-dimensional precise positioning system and method utilizing variation of optical speckle provided in the present invention are able to solve the problems mentioned above. It has advantages of wider applications and high precision.